The UN peacekeeping force, called the United Nations Interim Security Force for Abye (Unisfa) says “uniformed personnel” were spotted in Abyei on Tuesday.

It said it was "deeply worried" the development would further exacerbate the conflict and cause a humanitarian crisis for civilians living in the area.

South Sudan's army spokesperson, Maj Gen Lul Ruai Koang, has denied the presence of government soldiers in Abyei.

Unisfa said Abyei remains a “weapon-free area” that should not have the presence of any force.

“Unisfa condemns the renewed fighting within and around the borders of Abyei Box and urges all parties to ceasefire and allow the political process to resolve the lingering crisis,” it said in a statement.

It urged both countries to respect the UN Security Council resolution on demilitarization of Abyei.